Wireless inductive power transfer

ABSTRACT

An inductive power transfer system is arranged to transfer power from a power transmitter ( 101 ) to a power receiver ( 103 ) via a wireless power signal. The system supports communication from the power transmitter ( 101 ) to the power receiver ( 105 ) based on load modulation of the power signal. The power receiver ( 105 ) transmitting ( 507 ) a first message to the power transmitter ( 101 ) which comprises a standby power signal requirement for the power signal during a standby phase. The power transmitter ( 101 ) receives ( 507 ) the message, and when the system enters the standby phase, the power transmitter ( 101 ) provides the power signal in accordance with the standby power signal requirement during. A power receiver configurable standby phase is provided which may for example allow devices to maintain battery charge or to provide fast initialization of the power transfer phase.

FIELD OF THE INVENTION

The invention relates to inductive power transfer and in particular, butnot exclusively, to an inductive power transfer system compatible withthe Qi wireless power transfer approach.

BACKGROUND OF THE INVENTION

The number and variety of portable and mobile devices in use haveexploded in the last decade. For example, the use of mobile phones,tablets, media players etc. has become ubiquitous. Such devices aregenerally powered by internal batteries and the typical use scenariooften requires recharging of batteries or direct wired powering of thedevice from an external power supply.

Most present day systems require a wiring and/or explicit electricalcontacts to be powered from an external power supply. However, thistends to be impractical and requires the user to physically insertconnectors or otherwise establish a physical electrical contact. It alsotends to be inconvenient to the user by introducing lengths of wire.Typically, power requirements also differ significantly, and currentlymost devices are provided with their own dedicated power supplyresulting in a typical user having a large number of different powersupplies with each being dedicated to a specific device. Although, theuse of internal batteries may avoid the need for a wired connection to apower supply during use, this only provides a partial solution as thebatteries will need recharging (or replacing which is expensive). Theuse of batteries may also add substantially to the weight andpotentially cost and size of the devices.

In order to provide a significantly improved user experience, it hasbeen proposed to use a wireless power supply wherein power isinductively transferred from a transmitter coil in a power transmitterdevice to a receiver coil in the individual devices.

Power transmission via magnetic induction is a well-known concept,mostly applied in transformers, having a tight coupling between primarytransmitter coil and a secondary receiver coil. By separating theprimary transmitter coil and the secondary receiver coil between twodevices, wireless power transfer between these becomes possible based onthe principle of a loosely coupled transformer.

Such an arrangement allows a wireless power transfer to the devicewithout requiring any wires or physical electrical connections to bemade. Indeed, it may simply allow a device to be placed adjacent to oron top of the transmitter coil in order to be recharged or poweredexternally. For example, power transmitter devices may be arranged witha horizontal surface on which a device can simply be placed in order tobe powered.

Furthermore, such wireless power transfer arrangements mayadvantageously be designed such that the power transmitter device can beused with a range of power receiver devices. In particular, a wirelesspower transfer standard known as the Qi standard has been defined and iscurrently being developed further. This standard allows powertransmitter devices that meet the Qi standard to be used with powerreceiver devices that also meet the Qi standard without these having tobe from the same manufacturer or having to be dedicated to each other.The Qi standard further includes some functionality for allowing theoperation to be adapted to the specific power receiver device (e.g.dependent on the specific power drain).

The Qi standard is developed by the Wireless Power Consortium and moreinformation can e.g. be found on their website:http://www.wirelesspowerconsortium.com/index.html, where in particularthe defined Standards documents can be found.

The Qi wireless power standard describes that a power transmitter mustbe able to provide a guaranteed power to the power receiver. Thespecific power level needed depends on the design of the power receiver.In order to specify the guaranteed power, a set of test power receiversand load conditions are defined which describe the guaranteed powerlevel for each of the conditions.

Qi originally defined a wireless power transfer for low power devicesconsidered to be devices having a power drain of less than 5 W. Systemsthat fall within the scope of this standard use inductive couplingbetween two planar coils to transfer power from the power transmitter tothe power receiver. The distance between the two coils is typically 5mm. It is possible to extend that range to at least 40 mm.

However, work is ongoing to increase the available power, and inparticular the standard is being extended to mid-power devices beingdevices having a power drain of more than 5 W.

The Qi standard defines a variety of technical requirements, parametersand operating procedures that a compatible device must meet.

Communication

The Qi standard supports communication from the power receiver to thepower transmitter thereby enabling the power receiver to provideinformation that may allow the power transmitter to adapt to thespecific power receiver. In the current standard, a unidirectionalcommunication link from the power receiver to the power transmitter hasbeen defined and the approach is based on a philosophy of the powerreceiver being the controlling element. To prepare and control the powertransfer between the power transmitter and the power receiver, the powerreceiver specifically communicates information to the power transmitter.

The unidirectional communication is achieved by the power receiverperforming load modulation wherein a loading applied to the secondaryreceiver coil by the power receiver is varied to provide a modulation ofthe power signal. The resulting changes in the electricalcharacteristics (e.g. variations in the current draw) can be detectedand decoded (demodulated) by the power transmitter.

Thus, at the physical layer, the communication channel from powerreceiver to the power transmitter uses the power signal as a datacarrier. The power receiver modulates a load which is detected by achange in the amplitude and/or phase of the transmitter coil current orvoltage. The data is formatted in bytes and packets.

More information can be found in chapter 6 of part 1 the Qi wirelesspower specification (version 1.0).

Although Qi uses a unidirectional communication link, it has beenproposed to introduce communication from the power transmitter to thepower receiver. However, such a bidirectional link is not trivial toinclude and is subject to a large number of difficulties and challenges.For example, the resulting system still needs to be backwards compatibleand e.g. power transmitters and receivers that are not capable ofbidirectional communication still need to be supported. Furthermore, thetechnical restrictions in terms of e.g. modulation options, powervariations, transmission options etc. are very restrictive as they needto fit in with the existing parameters. It is also important that costand complexity is kept low, and e.g. it is desirable that therequirement for additional hardware is minimized, that detection is easyand reliable, etc. It is also important that the communication from thepower transmitter to the power receiver does not impact, degrade orinterfere with the communication from the power receiver to the powertransmitter. Furthermore, an all-important requirement is that thecommunication link does not unacceptably degrade the power transferability of the system.

Accordingly, many challenges and difficulties are associated withenhancing a power transfer system such as Qi to include bidirectionalcommunication.

System Control

In order to control the wireless power transfer system, the Qi standardspecifies a number of phases or modes that the system may be in atdifferent times of the operation. More details can be found in chapter 5of part 1 the Qi wireless power specification (version 1.0).

The system may be in the following phases:

Selection Phase

This phase is the typical phase when the system is not used, i.e. whenthere is no coupling between a power transmitter and a power receiver(i.e. no power receiver is positioned close to the power transmitter).

In the selection phase, the power transmitter may be in a standby modebut will sense to detect a possible presence of an object. Similarly,the receiver will wait for the presence of a power signal.

Ping Phase

If the transmitter detects the possible presence of an object, e.g. dueto a capacitance change, the system proceeds to the ping phase in whichthe power transmitter (at least intermittently) provides a power signal.This power signal is detected by the power receiver which proceeds tosend an initial package to the power transmitter. Specifically, if apower receiver is present on the interface of the power transmitter, thepower receiver communicates an initial signal strength packet to thepower transmitter. The signal strength packet provides an indication ofthe degree of coupling between the power transmitter coil and the powerreceiver coil. The signal strength packet is detected by the powertransmitter.

Identification & Configuration Phase

The power transmitter and power receiver then proceeds to theidentification and configuration phase wherein the power receivercommunicates at least an identifier and a required power. Theinformation is communicated in multiple data packets by load modulation.The power transmitter maintains a constant power signal during theidentification and configuration phase in order to allow the loadmodulation to be detected. Specifically, the power transmitter providesa power signal with constant amplitude, frequency and phase for thispurpose (except from the change caused by load-modulation).

In preparation of the actual power transfer, the power receiver canapply the received signal to power up its electronics but it keeps itsoutput load disconnected. The power receiver communicates packets to thepower transmitter. These packets include mandatory messages, such as theidentification and configuration packet, or may include some definedoptional messages, such as an extended identification packet or powerhold-off packet.

The power transmitter proceeds to configure the power signal inaccordance with the information received from the power receiver.

Power Transfer Phase

The system then proceeds to the power transfer phase in which the powertransmitter provides the required power signal and the power receiverconnects the output load to supply it with the received power.

During this phase, the power receiver monitors the output loadconditions, and specifically it measures the control error between theactual value and the desired value of a certain operating point. Itcommunicates these control errors in control error messages to the powertransmitter with a minimum rate of e.g. every 250 msec. This provides anindication of the continued presence of the power receiver to the powertransmitter. In addition the control error messages are used toimplement a closed loop power control where the power transmitter adaptsthe power signal to minimize the reported error. Specifically, if theactual value of the operating point equals the desired value, the powerreceiver communicates a control error with a value of zero resulting inno change in the power signal. In case the power receiver communicates acontrol error different from zero, the power transmitter will adjust thepower signal accordingly.

The system allows for an efficient setup and operation of the powertransfer. However, there are scenarios where the power transfer systemdoes not operate optimally.

For example, in the existing system, the power transmitter will enterthe ping phase from the selection phase when it is detected that a newpower receiver is introduced. However, if a power receiver device ise.g. permanently placed on the power transmitter, there is no initiatingevent, and the power receiver may remain in the selection phase and notbe able to re-enter the power transfer phase. This may be a problem fordevices that need repowering at intervals. For example, a batterypowered device may permanently be placed on a power transmitter. Afteran initial charging of the battery when the battery powered device isfirst put on the power transmitter, the system will enter the selectionphase. The device may be used while on the power transmitter and thebattery may be discharged. At some stage, it may be required that thebattery is recharged. However, as the system is in the selection phaseit will not be able to perform such a recharging.

In order to avoid such scenarios, it has been proposed for the powertransmitter to very occasionally enter the ping phase where it pings thepower receiver to see if a new power transfer phase should bere-initiated. However, this is expected to be performed at an intervalof several minutes which is too slow for many applications. Reducing thetime between the pings will increase power consumption for both powertransmitter and power receiver. Thus, reducing the time interval betweenpings to a value that is suitable for the most criticaldevice/application would result in a large overhead and increasedresource consumption which is completely unnecessary for the vastmajority of devices.

In order to address this, it has been proposed that the system may leavethe selection phase and initiate a new power transfer setup operation inresponse to receiving an active request from the power receiver.However, this requires that the power receiver can communicate an activemessage (i.e. it cannot use load modulation as there is no power signalprovided by the transmitter). Such an active initiation by the powerreceiver may be advantageous but requires that the power receiver hassufficient stored energy to generate the message. However, this requiresthat recharging of the devices, and thus the devices cannot continuouslyremain in the selection phase.

Specifically, it has been proposed that a power receiver can wake-up apower transmitter by applying an active signal. The power receiver usesan energy source (e.g. a battery) available in the power receiver togenerate the wake-up signal. However, not all devices contain a suitableenergy source. Furthermore, if an energy storage, like a battery or acapacitor is present, this may become discharged e.g. after intensiveuse of an application or after a considerable amount of time duringwhich a leakage or standby current has drained the available storedenergy. Therefore, recharging will be required.

More generally, whereas the conventional approach may provide verysuitable approaches for powering or charging a new power receiver whenthis is introduced, it tends to be relatively inflexible and not caterfor all scenarios in which a power receiver may want to extract powerfrom a power transmitter. Specifically, it merely allows the powerreceivers either to be powered by the power transmitter as part of astandard power transfer phase or to not be powered. However, manydevices have different requirements at different times and furthermorethese requirements can vary significantly between devices.

Hence, an improved power transfer system would be advantageous and inparticular a system allowing increased flexibility, backwardscompatibility, facilitated implementation, improved adaptation tovarying power requirements, and/or improved performance would beadvantageous.

SUMMARY OF THE INVENTION

Accordingly, the Invention seeks to preferably mitigate, alleviate oreliminate one or more of the above mentioned disadvantages singly or inany combination.

According to an aspect of the invention there is provided a method ofoperation for an inductive power transfer system comprising a powertransmitter generating a wireless power signal for a power receiver whenin a power transfer phase, the inductive power transfer systemsupporting communication from the power receiver to the powertransmitter based on load modulation of the power signal, the methodcomprising: the power receiver transmitting a first message to the powertransmitter, the first message comprising a standby power signalrequirement for the power signal during a standby phase; the powertransmitter receiving the message; and the power transmitter providingthe power signal in accordance with the standby power signal requirementduring the standby phase.

The invention may provide an improved power transfer system. It may inmany embodiments allow for further functionality and/or increasedperformance. An improved user experience may be provided. The inventionmay allow a practical approach and may facilitate introduction intoexisting systems.

The approach may introduce a standby phase intended for reduced powerconsumption, with the power receiver controlling the standby powerbehavior of the power transmitter.

In many embodiments, the approach may specifically allow improvedoperation for systems where the power receiver is coupled to the powertransmitter for extended amounts of time (including in particularmultiple (re)charge operations). In many scenarios, a faster activationof a power receiver device from a standby mode of operation can beachieved.

The power receiver may extract power from the power signal (and thusfrom the power transmitter) during the standby phase. The standby powersignal requirement may be a power requirement of the standby powersignal, such as a minimum amplitude or current that can be drawn by thepower receiver.

The approach is particularly advantageous in that the power receiver maycontrol the operation of the power transmitter when in the standby phaseso that this provides a power signal that meets the specificrequirements and preferences of the power receiver (or a device poweredby the power receiver). The power receiver may for example control thepower transmitter to provide sufficient power for the power receiver tomaintain the reduced functionality of the standby phase, and/or it maycontrol characteristics of the power signal such that it allows thepower receiver to wake-up the power transmitter sufficiently fast, andspecifically such that the power transfer phase can be enteredsufficiently fast but without excessive resource usage. For example,time intervals between the power signal being switched on to allow loadmodulation may be controlled to suit the specific power receiver (orassociated device).

The approach is furthermore in line with the general design principlesof power transfer systems such as Qi in that it allows the main controlto reside with the power receiver.

The approach may also be relatively easy to introduce to systems such asQi. For example, it may be implemented using only uni-directionalcommunication from the power receiver to the power transmitter.

In the standby phase, the power receiver operates in a reduced powermode. The power consumption of the power receiver when in the standbyphase is reduced with respect to the power consumption of the powerreceiver when in the power transfer mode. The power receiver may in thestandby phase perform a reduced functionality. Typically, the reducedfunctionality may be limited to functionality that allows the system tobe initialized to enter a nominal operating mode (specifically thereduced functionality may be limited to wake-up functionality).Specifically, the load may be disconnected by the power receiver when inthe standby phase. In the power transfer phase, the load will beconnected.

In some scenarios, the system may operate a power control loop when inthe power transfer phase but not when in the standby phase.

The term power receiver will be understood to refer to the functionalityimplemented to enable and perform the wireless power transfer. It willalso be understood that the term may refer to the entire functionalitypowered by the wireless power transfer, and specifically that it mayinclude the load. Specifically, the term may include an entire devicesupported by the wireless power transfer, such as e.g. a communicationor computational device powered via the wireless power transfer. Theterm may include such broader functionality independently of whether itis implemented in a single unit or in a plurality of (physical orfunctional) units.

The standby phase may comprise other phases or sub-phases. For example,the standby phase may comprise or consist in a selection phase and aping phase for a Qi type system.

In accordance with an optional feature of the invention, the standbypower signal requirement is indicative of a power requirement of thepower signal during the standby phase.

This may be particularly advantageous in many scenarios. The powerreceiver may specifically control the power transmitter to provide apower signal that allows the power receiver to extract the desired powerfrom the power signal but without excessive resource usage. For example,the power requirement may be a required power level, and especially maybe an average or minimum power level. In some scenarios, the powersignal may be continuously applied and the power level may be acontinuous value. In some embodiments, the power signal may bediscontinuous and the standby power requirement may indicate a temporalcharacteristic of the provided power.

In accordance with an optional feature of the invention, the standbypower signal requirement represents a minimum power for a reducedfunctionality of the power receiver.

This may be particularly advantageous and may allow the system to beoptimized to provide sufficient power to support the reducedfunctionality of the power receiver when in the standby phase butwithout unnecessarily wasting resource.

In some embodiments, the power receiver may determine the standby powersignal requirement in response to a power consumption for a reducedfunctionality of the power receiver.

In accordance with an optional feature of the invention, the reducedfunctionality comprises functionality for initializing a wake-up processfor the power receiver.

This may in particular allow power consumption to be reduced, and oftensubstantially minimized, while still allowing the power receiver (orattached device) to quickly and efficiently be returned to anoperational mode, and specifically to the power transfer phase.

The wake-up process may specifically be a process that transfers thesystem to the power transfer phase. The wake-up process may specificallybe an active wake-up process wherein the power receiver transmits aninitialization message to the power transmitter without using loadmodulation of the power signal, or may e.g. be passive wake-up processwherein the power receiver transmits messages to the power transmitterby load modulating the power signal.

In accordance with an optional feature of the invention, the powerrequirement represents a minimum power for maintaining an energy storagerequirement for the power receiver during the standby phase.

This may be a particularly advantageous approach. The system mayspecifically ensure that the power receiver can enter a standby phasewhere power consumption is reduced while still ensuring that the energystored in the power receiver remains sufficient. Specifically, theapproach allows a standby phase with low power consumption while stillensuring that a battery of the power receiver is kept charged to adesired extent, thereby ensuring that the power receiver device remainsoperational.

In accordance with an optional feature of the invention, the powertransmitter is arranged to provide the power signal intermittentlyduring the standby phase, and the standby power signal requirement isindicative of a timing of time intervals in which the power signal isprovided.

This may in many embodiments reduce resource consumption and/or reducefunctionality. For example, it may allow the trade-off between powerconsumption and time to initialize a new power transfer to be optimizedfor the preferences and requirements of the specific power receiver(including the device being powered by the power receiver).

The intermittent power signal may be used to transfer power to the powerreceiver and/or to provide a signal allowing the power receiver tocommunicate by load modulation. Indeed, the intermittent power signalmay be used to ping the power receiver and/or to power the powerreceiver during the standby phase.

In accordance with an optional feature of the invention, the powerreceiver transmits a wake-up message to the power transmitter during thestandby phase; and the power transmitter moves to the power transferphase in response to receiving the wake-up message.

This may allow advantageous operation. The power receiver may enter thepower transfer phase in response to transmitting the wake-up message ore.g. in response to receiving a confirmation of the message from thepower transmitter.

In some embodiments, the system may move directly to the power transferphase without any configuration phase being applied. In someembodiments, the system may move to the power transfer phase via one ormore intervening phases, such as an intervening ping or configurationphase. In such embodiments, the entering of the power transfer phase maybe conditional on the operation in the intervening phases. Thus, thesystem may only proceed to the power transfer phase in some scenarios(e.g. conditional on an appropriate response by the power receiver inthe ping phase).

Thus, the power transfer phase may be initiated using the configurationparameters set prior to the wake up.

In accordance with an optional feature of the invention, the wake-upmessage is transmitted from the power receiver by load modulation of thepower signal during the standby phase.

This may provide efficient operation in many embodiments. Specifically,the power consumption during the standby phase may be reduced. Forexample, it may allow a power signal to be provided which isinsufficient to power the (reduced) functionality of the power receiverbut is sufficient to support load modulation. The reduction in power mayallow the power signal to be provided with a much higher frequencythereby allowing a much faster wake-up of the system.

In some embodiments, the wake-up message is transmitted by the powerreceiver using functionality powered from an internal energy store ofthe power receiver.

This may provide improved performance in some scenarios. In particular,the power receiver may transmit the wake up message without the powertransmitter needing to provide a power signal for this purpose.

In accordance with an optional feature of the invention, the powerreceiver determines an energy storage level for an energy store of thepower receiver and transmits a second message to the power transmitterduring the standby phase if the energy storage level is below athreshold; and wherein the power receiver and the power transmitterinitiate a power transfer operation if the second message istransmitted.

This may provide advantageous performance and may in particular allow anefficient way of maintaining sufficient energy in the power receiverwithout requiring the standby phase to provide power transfer. Thus, thenormal power transfer operation is used but it may be applied simply torecharge an energy storage (such as e.g. a capacity holding a chargesufficient to power part of the functionality for a short timeinterval).

In accordance with an optional feature of the invention, the firstmessage indicates a maximum duration of an interval in the standby phasein which no power signal is provided by the power transmitter.

This may provide efficient performance in many scenarios and may inparticular in many embodiments facilitate introduction of the standbyphase to existing systems. Specifically, it may provide an efficient wayof implementing the standby phase using the selection phase and the pingphase of the Qi systems. The first message may provide a timingindication for when to switch between the selection phase and the pingphase, such as e.g. a maximum duration of the selection phase.

In accordance with an optional feature of the invention, the powerreceiver sets a power level for the power signal by transmitting powercontrol error messages at the end of the power transfer phase, and thestandby power signal requirement is indicative of a requirement tomaintain the power level during the standby phase.

This may provide efficient yet low complexity operation.

In accordance with an optional feature of the invention, the powerreceiver is arranged to transmit the first message during the powertransfer phase.

This may provide efficient yet low complexity operation in manyembodiments and may in particular allow robust operation with efficientsignaling.

In accordance with an optional feature of the invention, the powertransmitter is arranged to enter the standby phase in response toreceiving an end of power transfer phase message.

This may provide efficient yet low complexity operation in manyembodiments and may in particular allow robust operation with efficientsignaling.

In accordance with an optional feature of the invention, the powerreceiver charges an internal energy store from the power signal duringthe standby phase.

This may provide advantageous performance and may in particular allow anefficient way of maintaining sufficient energy in the power receiver.

In accordance with an optional feature of the invention, the powertransmitter and power receiver switches from the standby phase to thepower transfer phase without entering a configuration phase.

This may in many scenarios allow a more efficient and/or in particularfaster wake-up of the power receiver. Thus, the power transfer phase maybe initiated using configuration parameters set prior to the wake-up.

In some embodiments, the power transmitter and power receiver switchesfrom the standby phase (directly) to a ping phase.

In some embodiments, the power transmitter and power receiver switchesfrom the standby phase (directly) to a configuration phase.

In accordance with an optional feature of the invention, the powerreceiver is arranged to transmit the first message during aconfiguration phase occurring prior to the power transfer phase.

This may provide efficient yet low complexity operation in manyembodiments and may in particular allow robust operation with efficientsignaling. The approach may allow the configuration of the standby phaseto be performed in accordance with the same principles and approaches asconfiguration procedures for other parameters. This may for exampleallow reuse of functionality.

In accordance with an optional feature of the invention, the powerreceiver is arranged to transmit a second message to the powertransmitter indicating an activity to be performed by the powertransmitter in response to receiving a wake-up message.

This may provide a more flexible system and may allow the operation ofthe system to be adapted to the specific requirements and preferences ofthe individual power receiver. For example, the power receiver maydefine or request that the power transmitter enters the power transferphase directly without entering a configuration phase after waking upfrom the standby mode, or that it should enter the configuration phasefirst. In some embodiments, the power receiver may command or requestthat the power transmitter responds to a wake-up message by providing apower signal which can be power modulated by the power receiver.

In some embodiments, the second message indicates a phase that the powertransmitter should enter after a wake-up from the standby phase.

In some embodiments, the second message indicates whether the powertransmitter should skip a configuration phase between the standby phaseand the power transfer phase.

According to an aspect of the invention there is provided a method ofoperation for a power transmitter of an inductive power transfer systemcomprising the power transmitter and a power receiver, the inductivepower transfer system supporting communication from power receiver tothe power transmitter based on load modulation of the power signal, themethod comprising: generating a wireless power signal for a powerreceiver when in the power transfer phase; receiving a first messagecomprising a standby power signal requirement for the power signalduring a standby phase; and providing the power signal in accordancewith the standby power signal requirement during a standby phase.

According to an aspect of the invention there is provided method ofoperation for a power receiver of an inductive power transfer systemcomprising a power transmitter for generating a wireless power signalfor the power receiver when in a power transfer phase, the inductivepower transfer system supporting communication from the power receiverto the power transmitter based on load modulation of the power signal,the method comprising: extracting power from the power signal when inthe power transfer phase; transmitting a first message to the powertransmitter, the first message comprising a standby power signalrequirement for the power signal during a standby phase; and receivingthe power signal when in the standby phase.

According to an aspect of the invention there is provided an inductivepower transfer system comprising a power transmitter and a powerreceiver, the inductive power transfer system being arranged to transferpower from the power transmitter to the power receiver via a wirelesspower signal and supporting communication from the power receiver to thepower transmitter based on load modulation of the power signal, whereinthe power receiver comprises a transmitter for transmitting a firstmessage to the power transmitter, the first message comprising a standbypower signal requirement for the power signal during a standby phase;and the power transmitter comprises: a power unit for generating thepower signal to provide power transfer to the power receiver when in apower transfer phase: a receiver for receiving the first message; and astandby unit for providing the power signal in accordance with thestandby power signal requirement during the standby phase.

According to an aspect of the invention there is provided a powertransmitter for an inductive power transfer system comprising the powertransmitter and a power receiver, the inductive power transfer systemsupporting communication from the power receiver to the powertransmitter based on load modulation of the power signal, the powertransmitter comprising: a generator for generating a wireless powersignal for the power receiver when in a power transfer phase; a receiverfor receiving a first message comprising a standby power signalrequirement for the power signal during a standby phase; and a standbyunit for providing the power signal in accordance with the standby powersignal requirement during the standby phase.

According to an aspect of the invention there is provided a powerreceiver for an inductive power transfer system comprising a powertransmitter for generating a wireless power signal for the powerreceiver when in a power transfer phase, the inductive power transfersystem supporting communication from the power receiver to the powertransmitter based on load modulation of the power signal, the powerreceiver comprising: a power unit for extracting power from the powersignal when in the power transfer phase; a transmitter for transmittinga first message to the power transmitter, the first message comprising astandby power signal requirement for the power signal during a standbyphase; and a receiver for receiving the power signal when in the standbyphase.

These and other aspects, features and advantages of the invention willbe apparent from and elucidated with reference to the embodiment(s)described hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will be described, by way of example only,with reference to the drawings, in which

FIG. 1 provides an exemplary illustration of a power transfer system inaccordance with some embodiments of the invention;

FIG. 2 provides an exemplary illustration of a power transmitter inaccordance with some embodiments of the invention;

FIG. 3 provides an exemplary illustration of a power receiver inaccordance with some embodiments of the invention;

FIG. 4 provides an exemplary illustration of a power receiver inaccordance with some embodiments of the invention; and

FIG. 5 provides an exemplary illustration of a method of operation for apower transfer system in accordance with some embodiments of theinvention.

DETAILED DESCRIPTION OF SOME EMBODIMENTS OF THE INVENTION

FIG. 1 illustrates an example of a power transfer system in accordancewith some embodiments of the invention. The power transfer systemcomprises a power transmitter 101 which includes (or is coupled to) atransmitter coil/inductor 103. The system further comprises a powerreceiver 105 which includes (or is coupled to) a receiver coil/inductor107.

It will be appreciate that the power receiver 105 may e.g. be a singleintegrated device providing both a user functionality (e.g. acommunication or computational function) as well as the powertransfer/extracting functionality. In other scenarios, the powerreceiver 105 may only comprise the functionality for extracting powerwith the power being provided to an external load. In the following theterm power receiver 105 will be used to denote both the powertransfer/extraction functionality in itself, as well as the combinedfunctionality of the power transfer/extraction functionality and a loadpowered by this functionality. Specifically, the term will also refer toa combination of a power transfer device and a user device powered bythe power transfer device.

The system provides a wireless inductive power transfer from the powertransmitter 101 to the power receiver 105. Specifically, the powertransmitter 101 generates a power signal which is propagated as amagnetic flux by the transmitter coil 103. The power signal maytypically have a frequency between around 100 kHz to 200 kHz. Thetransmitter coil 103 and the receiver coil 105 are loosely coupled andthus the receiver coil picks up (at least part of) the power signal fromthe power transmitter 101. Thus, the power is transferred from the powertransmitter 101 to the power receiver 105 via a wireless inductivecoupling from the transmitter coil 103 to the receiver coil 107. Theterm power signal is mainly used to refer to the electrical signalprovided to the transmitter coil 103 but it will be appreciated that byequivalence it may also be considered and used as a reference to themagnetic flux signal, or indeed to the electrical signal of the receivercoil 107.

In the following, the operation of the power transmitter 101 and thepower receiver 105 will be described with specific reference to anembodiment in accordance with the Qi standard (except for the hereindescribed (or consequential) modifications and enhancements). Inparticular, the power transmitter 101 and the power receiver 103 maysubstantially be compatible with the Qi Specification version 1.0 or 1.1(except for the herein described (or consequential) modifications andenhancements).

To prepare and control the power transfer between the power transmitter101 and the power receiver 105 in the wireless power transfer system,the power receiver 105 communicates information to the power transmitter101. Such communication has been standardized in the Qi Specificationversion 1.0 and 1.1.

On physical level, the communication channel from the power receiver 105to the power transmitter 101 is implemented by using the power signal ascarrier. The power receiver 105 modulates the load of the receiver coil105. This results in corresponding variations in the power signal at thepower transmitter side. The load modulation may be detected by a changein the amplitude and/or phase of the transmitter coil 105 current, oralternatively or additional by a change in the voltage of thetransmitter coil 105. Based on this principle, the power receiver 105can modulate data which the power transmitter 101 demodulates. This datais formatted in bytes and packets. More information can be found in the“System description, Wireless Power Transfer, Volume I: Low Power, Part1: Interface Definition, Version 1.0 July 2010, published by theWireless Power Consortium” available viahttp://www.wirelesspowerconsortium.com/downloads/wireless-power-specification-part-1.html,also called the Qi wireless power specification, in particular chapter6: Communications Interface.

To control the power transfer, the system may proceed via differentphases, in particular a selection phase, a ping phase, identificationand configuration phase, and a power transfer phase. More informationcan be found in chapter 5 of part 1 of the Qi wireless powerspecification.

Initially, the power transmitter 101 is in the selection phase whereinit merely monitors for the potential presence of a power receiver. Thepower transmitter 101 may use a variety of methods for this purpose,e.g. as described in the Qi wireless power specification. If such apotential presence is detected, the power transmitter 101 enters theping phase wherein a power signal is temporarily generated. The powerreceiver 105 can apply the received signal to power up its electronics.After receiving the power signal, the power receiver 105 communicates aninitial packet to the power transmitter 101. Specifically, a signalstrength packet indicating the degree of coupling between powertransmitter and power receiver is transmitted. More information can befound in chapter 6.3.1 of part 1 of the Qi wireless power specification.Thus, in the Ping phase it is determined whether a power receiver 105 ispresent at the interface of the power transmitter 101.

Upon receiving the signal strength message, the power transmitter 101moves into the identification & configuration phase. In this phase, thepower receiver 105 keeps its output load disconnected and communicatesto the power transmitter 101 using load modulation. The powertransmitter provides a power signal of constant amplitude, frequency andphase for this purpose (with the exception of the change caused byload-modulation). The messages are used by the power transmitter 101 toconfigure itself as requested by the power receiver 105.

The system then moves on to the power transfer phase where the actualpower transfer takes place. Specifically, after having communicated itspower requirement, the power receiver 105 connects the output load andsupplies it with the received power. The power receiver 105 monitors theoutput load and measures the control error between the actual value andthe desired value of a certain operating point. It communicates suchcontrol errors to the power transmitter 101 at a minimum rate of e.g.every 250 ms to indicate these errors to the power transmitter 101 aswell as the desire for a change, or no change, of the power signal.

It is noted that the Qi wireless power specification versions 1.0 and1.1 define only communication from the power receiver 105 to the powertransmitter 101, i.e. it defines only a unidirectional communication.

However, in the system of FIG. 1 bidirectional communication is used,i.e. communication of data is also possible from the power transmitter101 to the power receiver 105. Various applications may benefit fromsuch communication, for example: setting a power receiver in test mode,setting a power receiver in calibration mode, or allowing communicationfrom power transmitter to power receiver under the control of the powerreceiver, e.g. for communicating a command, or status information frompower transmitter to power receiver.

Although the bi-directional communication may provide advantages in manyscenarios and embodiments, this is merely an optional feature. Indeed,the principles and operation described in the following may beimplemented without using or relying on communication from the powertransmitter 101 to the power receiver 105.

FIG. 2 illustrates the power transmitter 101 of FIG. 1 in more detail.The transmitter coil 103, also called the primary coil 103 (PCL), isshown connected to a power transmitter communication unit 201 (TRM-COM),which is coupled to a transmitter controller 203 (CTR).

The power transmitter communication unit 201 has a modulator 205 (MOD),coupled to a driver 207 (DRV) for driving the transmitter coil 103 fortransmitting a (potentially) modulated power signal (PS) via thetransmitter coil 103 to the receiver coil 105. The driver 207 is coupledto the transmitter controller 203 which may control the driver toprovide a power signal to have the desired characteristics, such as adesired power level (amplitude and/or current). The power signal is thusdependent on both the control from the controller as well as(optionally) on the modulation by the modulator 205 if the power signalis also used to communicate a message from the power transmitter 101 tothe power receiver 105.

In the system, the power receiver 105 may load modulate the power signalto send a power receiver signal to the power transmitter 101 via thereceiver coil 107 and the transmitter coil 103. This signal is called areflected signal (RS). The reflected signal is detected by a sense unit209 (SNS), e.g. by sensing the current or voltage on the transmittercoil 103. A demodulator 211 (DEM) is coupled to the transmittercontroller 203 for demodulating the detected signal, e.g. by convertingchanges in the amplitude or phase of the detected signal into bits.

In the example of FIG. 2, a first unit 213 is arranged to receive datafrom the power receiver 105 via the transmitter coil 103. The first unit213 comprises the sense unit 209 and the demodulator 211. These twounits implement the function of receiving the data via the transmittercoil 103. The transmitter coil 103 transmits an alternating magneticfield (the power signal PS) for inductive power transfer to the receivercoil 107 and receives the reflected magnetic field (reflected signal RS)caused by the receiver coil 107 (i.e. the variations in the power signalcaused by the load modulation). The sense unit 209 (current/voltagesensor SNS) senses the current/voltage on the transmitter coil 103. Thedemodulator 211 translates changes of amplitude or phase of the sensedsignal into data.

The transmitter controller 203 interprets the received data and may inresponse control a second unit 205 to transmit a message to the powerreceiver 105 via the transmitter coil 103. The message may in theexample specifically be a response message intended for responding tomessages from the power receiver 105, and may specifically be anacknowledge/non-acknowledge or accept/reject message. Such acommunication arrangement may allow a low complexity approach and mayavoid the need for complex communication functionality and protocols forsupporting the power transmitter to power receiver communication. Theapproach may further allow the power receiver to remain the controllingelement for the power transfer, and thus fits well with the generaldesign principles of the Qi power transfer approach.

Specifically, the transmitter controller 203 controls the modulator 205which modulates the power signal to provide the desired message. Themodulator 205 may specifically modulate the power signal by changing theamplitude, frequency, or phase of the power signal, i.e. it maytypically use AM, FM and/or PM modulation. The driver 207, alsocomprised by the second unit 215, is arranged to transmit the modulatedpower signal via the transmitter coil 103 to the power receiver 105 bysupplying an alternating electric signal to the transmitter coil 103.

The controller 203 is further arranged to control the power transfersettings and to implement the required control and operational phasesand functionality. In particular, the controller 203 may receive andinterpret the messages from the power receiver 103, and may in responsee.g. set the required power level for the power signal. Specifically,during the identification and configuration phase, the controller 203may interpret the configuration packet or message from the powerreceiver 105 and may e.g. set the maximum power signal levelaccordingly. During the power transfer phase, the transmitter controller203 may increase or decrease the power level in accordance with thecontrol error messages received from the power receiver 105.

FIG. 3 illustrates the power receiver 105 of FIG. 1 in more detail. Thereceiver coil 107 (SCL) is shown connected to a power receivercommunication unit 301 (REC-COM), which is coupled to a receivercontroller 303 (CTR). The power receiver 105 comprises a first unit 305for sending data to the power transmitter 101 via the receiver coil 107to the transmitter coil 103. The first unit 305 has a changeable load(LD) 307 coupled to a modulator 309 (MOD) for modulating the load at thereceiver coil 107 for generating the reflected signal (RS) fortransmitting data to the power transmitter 101. It will be understoodthat the first unit 305 is a functional unit that comprises themodulator 309 and the changeable load 307.

The power receiver 105 further comprises a second unit 311 for receivinga message from the power transmitter 101 via the receiver coil 107. Forthis purpose, the second unit 311 comprises a sense unit 313 (SNS) fordetecting a modulated power signal (PS) received via the receiver coil107 from the power transmitter 101, e.g. by sensing a voltage orcurrent.

The second unit 311 further comprises a demodulator 315 (DEM), which iscoupled to the sense unit 313 and the receiver controller 303. Thedemodulator 315 demodulates the detected signal according to the usedmodulation. The modulation may for example be an Amplitude Modulation(AM), Phase Modulation (PM) or Frequency Modulation (FM), and thedemodulator 315 may perform the appropriate demodulation to obtain themessage, e.g. by converting changes in the amplitude, frequency and/orphase of the detected signal into bits.

As an example, the receiver coil 107 may receive the power signal forinductive power transfer from the transmitter coil 103 and may send areflected signal to the transmitter coil 103 by varying the load 307.Thus, the variations of the load 307 provide the modulation of the powersignal. The modulator 309 controls the amplitude (and/or frequencyand/or phase of the reflected signal), i.e. it controls the operation ofthe load 307, e.g. by connecting/disconnecting an impedance circuit. Thecurrent/voltage sense unit 313 senses the current/voltage on thereceiver coil 107 as received from the power transmitter 101. The senseunit 313 may be part of another function of the power receiver andspecifically may be part of the rectification and smoothing of the powersignal used to generate a DC power. The demodulator 315 translateschanges of the sensed signal into data. The receiver controller 303(amongst other things) controls the modulator 309 to communicate dataand interprets the data received by the demodulator 315.

The power receiver coil 107 is further connected to a power unit 317which is arranged to receive the power signal and to extract the powerduring the power transfer phase. The power unit 317 is coupled to apower load 319 which is the load powered from the power transmitter 101during the power transfer phase. The power load 319 may be an externalpower load but is typically part of the power receiver device, such as abattery, display or other functionality of the power receiver (e.g. fora smart phone the power load may correspond to the combinedfunctionality of the smart phone).

The power receiver coil 107 may specifically include a rectifiercircuit, a smoothing circuit (a capacitor) and a voltage (and/orcurrent) regulation circuit in order to provide a stabilized DC outputvoltage (or current) supply.

The power unit 317 is coupled to the receiver controller 303. Thisallows the receiver controller 303 to determine the operationalcharacteristics of the power circuit and e.g. may be used to provideinformation on the current operating point to the receiver controller303. The receiver controller 303 may use this to generate the controlerror messages during the power transfer phase. The receiver controller303 may further control the operation of the power unit 317, e.g. thereceiver controller 303 may switch the load in and out. Specifically,the receiver controller 303 may control the power unit 317 to disconnectthe load during the configuration phase and connect it during the powertransfer phase.

In the system of FIG. 3, the sense unit 313 is shown to directly receivethe power signal and the second unit 311 demodulates the data directlyfrom the power signal. This may for example be useful for frequencymodulation.

However, in many scenarios the sense unit 313 may not directly sense thepower signal but rather a signal of the power unit 317.

As a specific example, the sense unit 313 may measure the rectified andsmoothed voltage generated by the power unit 317. This may beparticularly suitable for AM modulation of the power signal.

Specifically, FIG. 4 illustrates elements of the power unit 317 in moredetail. The signal from the receiver coil 107 is rectified by arectifier 401 (typically a bridge rectifier) and the resulting signal issmoothed by the capacitor C_(L) resulting in a smoothed DC voltage (witha ripple depending on the power consumption and value of CL). FIG. 4furthermore shows a switch S_(L) for switching the power load 319 in andout. In order to ensure a sufficiently low ripple during power transferthe capacitor C_(L) is typically selected to be relatively high therebyleading to a slow time constant for capacitor and load combination.

In the example, the power transmitter 101 may apply amplitude modulationto the power signal in order to communicate from the power transmitter101 to the power receiver 105. This will result in amplitude changesacross the capacitor C_(L), and in the example the sense unit 313 iscoupled to measure this voltage. Thus, the voltage variations across thecapacitor C_(L) may be detected and used to recover the data modulatedonto the power signal. Using such an approach may reduce cost andcomplexity as it allows components to be reused.

In contrast to conventional power transfer systems, the system of FIG. 1may provide additional functionality and an improved user experience,especially for power receivers being coupled to the power transmitter101 for extended durations (typically significantly longer than the timespent in the power transfer phase). The system may specifically supportthe Qi Standard version 1.0 and 1.1 but be enhanced to provideadditional functionality.

Specifically, the system provides for a standby phase wherein the powertransmitter 101 provides a power signal with properties that have beendefined by the power receiver 105. In particular, the power receiver 105transmits a message which comprises a standby power signal requirementfor the power signal during a standby phase. The power transmitter 101receives the message and interprets the standby power signalrequirement. When the power transmitter 101 then enters the standbyphase, it proceeds to generate a power signal that matches therequirement.

Thus, the system can operate be in a standby phase wherein a powersignal is still generated and can be used by the power receiver 105(e.g. to maintain the charge of an internal battery). Furthermore, thecharacteristics of the power signal are controlled by the power receiver105 such that the power signal can be adapted to the specificrequirements of the power receiver 105. This may not only provideimproved performance and adaptation but may typically also substantiallyreduce the power consumption during the standby power phase and/or e.g.reduce the wake up time for the receiver.

Typically, the power receiver 105 may transmit a message which resultsin the power transmitter 101 generating a small amount of power duringthe standby phase which can then be extracted to support a reduced lowpower functionality during this phase. As a specific example, theapproach may allow a standby power transfer to be used to charge abattery in a mobile device while this is in a standby mode of operation.

During the ping, identification & configuration and power transfer phasethe system can be regarded to be in normal operational mode wherein thepower receiver may control the power transmitter. The selection phasecan be regarded as the phase for reduced power consumption wherein thepower transmitter may decide to enter the ping phase (as part of thestandby phase) for providing a power signal or not. The approach thusintroduces a standby phase suitable for reduced power consumption and inwhich the standby power behavior of the power transmitter is controlledby the power receiver.

FIG. 5 illustrates an example of the operation of the power transfersystem of FIG. 1.

Initially, the power transmitter 101 is in the selection phase 501wherein no power signal is generated and the power transmitter 101 iseffectively in a dormant mode of operation. However, the powertransmitter 101 still monitors for the presence of a power receiver 105.If it detects the potential presence of a power receiver 105, it entersthe ping phase 503. The detection may for example be based on adetection of a change in capacitance, etc.

In the ping phase 503, the power transmitter 101 temporarily powers upfor a short duration. This signal may power the power receiver 105 (orat least indicate the presence of the power transmitter 101 to the powerreceiver 105), and in response the power receiver 105 enters the pingphase 505. The power receiver 105 then transmits a signal strengthmessage to the power transmitter 101 by load modulation of the powersignal. The message may indicate that no power transfer is required inwhich case the power transmitter 101 returns to the selection phase 501.If the power receiver 105 does require the initiation of a powertransfer, the message will indicate so. In this case, the power receiver105 enters a configuration phase 507 after having transmitted the signalstrength message, and the power transmitter 101 enters the configurationphase 509 in response to receiving the message.

The power transmitter 101 and power receiver 105 then proceed to performthe configuration phase 507, 509 to establish a first set of powertransfer parameters. Specifically, the power receiver may provide anidentification of itself (such as by a version number) and a powertransfer value may be defined.

In the configuration phase 507, 509 messages are exchanged between thepower receiver 105 and the power transmitter 101 to establish operatingparameters, and in particular operating parameters for the powertransfer operation.

The configuration phase 507, 509 may specifically be based onunidirectional communication from power receiver 105 to powertransmitter 101. In particular, the configuration phase 507, 509 maycorrespond to the Identification & Configuration phase as defined by theQi specification version 1.0 and 1.1. Specifically, the power receiver105 may provide an identification of itself (such as by a versionnumber) and a power transfer value may be defined.

Alternatively or additionally, the configuration phase may include abidirectional message exchange that allows various operating parametersto be defined. Thus, in some embodiments the configuration phase 507,509 may also utilize communication of messages from the powertransmitter 101 to the power receiver 105.

For example, the configuration phase may first comprise auni-directional configuration subphase such as the Identification &Configuration defined by the Qi specification version 1.0 and 1.1. Thismay be followed by a bidirectional negotiation phase wherein the powertransmitter 101 and power receiver 105 may negotiate parameters. Thenegotiation phase may specifically be based on the power receiver 105transmitting requests to the power transmitter 101 and the powertransmitter 101 responding to each request with a message accepting orrejecting the proposed parameter.

The negotiation phase may be optional, and specifically may only beentered if both devices are capable of supporting such a phase. Forexample, the power transmitter 101 and/or power receiver 105 may becapable of performing a Qi version 1.0 or 1.1 configuration with anycorresponding Qi version 1.0 or 1.1 device. However, if both devices arecapable of supporting a negotiation phase (which is not part of the Qispecification version 1.0 or 1.1), the devices may perform thenegotiation phase to determine and configure more parameters thanpossible when complying with the Qi Specification version 1.0 or 1.1.The approach may thus provide backwards compatibility while providingenhanced functionality for suitably capable devices.

More description of such a negotiation phase may be found in U.S.61/665,989 which is hereby incorporated in its entirety by reference.

Following the configuration phase 507, 509, the power transmitter 101and power receiver 105 move into the power transfer phase 511, 513wherein the power receiver 105 is powered by the power transmitter 101.The power transfer is performed using the parameters set in theconfiguration phase 507, 509.

In conventional systems, the system would return to the selection phase501 following the termination of the power transfer phase 511, 513. Thesystem would then remain in the selection phase. However, the powerreceiver 105 may be a device staying in the same position for extendedperiods (e.g. a lamp or a communication or computing device beingpositioned on the power transmitter may remain there for a very longtime (e.g. a laptop may normally be used when placed on a powertransmitter positioned on an office desk and only occasionally removedtherefrom)). In such scenarios the battery of the device would graduallydischarge due to power being consumed by some circuitry or simply due toleakage currents. Furthermore, as there is no change in the location ofthe power receiver, the power transmitter cannot use this to initiate anew power cycle.

It has been proposed that the power transmitter may enter the ping phaseat predetermined time intervals to investigate if a power receiver needsfurther power. However, this will tend to either result in an efficientoperation with typically unnecessarily high power consumption, and/or toresult in the delay in waking up the power transmitter being too longfor the power receiver (e.g. proposed times have been around every fiveminutes to reduce power consumption). To address such issues, it hasbeen proposed that the power receiver may send an active message to thepower transmitter without a power signal being present. An activemessage is communicated from the power receiver 105 to the powertransmitter 101 using energy provided by the power receiver 105. Thus,it is not just a passive load modulation of a power signal provided bythe power transmitter 101 but is a message communicated by a signalgenerated by the power receiver 105. Indeed, the active message cannotuse passive load modulation (as there may not be any power signal) butmust be based on the power receiver generating a signal that is fed tothe receiver coil 107 and picked by the transmitter coil 103. However,such an approach requires the power receiver to have an internal energystore. Such an internal energy store will inherently be discharged withtime.

In the system of FIG. 1, the power transmitter 101 and the powerreceiver 105 may enter a standby phase 515, 517 in which a standby powersignal is still provided by the power transmitter 101 but in accordancewith specific requirements that have been communicated to the powertransmitter 101 from the power receiver 105. Thus, the operation of thepower transmitter 101 in the standby phase 515, 517 can be optimized forthe specific power receiver 105. In the system, the power receiver 105specifically transmits a requirement message to the power transmitter101 which contains a standby power signal requirement indicating one ormore characteristics required of the power signal when the systemoperates in the standby phase. The requirement message may be adedicated message or may be a message in which the standby power signalrequirement is included together with other data. The requirementmessage may for example be communicated as part of the configurationphase 507, 509 (e.g. as part of a negotiation subphase thereof) or maye.g. be communicated as part of the power transfer phase 511, 513.

As a very specific example, during the configuration phase 507, 509, thepower receiver 105 may communicate a requirement that during a standbyphase 515, 517, a power signal with a specific reduced power level whichis suitable for trickle charging a battery of the power receiver 105should be provided. The power transmitter 101 will then provide such areduce power level power signal during the standby phase 515, 517 andthe power receiver 105 will use this to keep the battery charged. Thismay for example ensure that the power receiver 105 is always able totransmit an active wake up message.

In the standby phase 515, 517 the power receiver 105 operates in areduced functionality/reduced power consumption mode. Typically, themain functionality of the power receiver 105 is switched off during sucha standby mode, and particularly the load 319 is disconnected from thepower unit 317. Specifically, the power receiver 105 may in the standbyphase 515, 517 only power the functionality required for maintaining anenergy store of the power receiver 105 and for interfacing with thepower transmitter 101.

In many embodiments, the standby power signal requirement may include anindication of a standby power requirement, and specifically of a powerlevel that should be provided by the power transmitter 101 during thestandby phase 515, 517. The power level may for example be a minimumpower level which the power signal should provide in order to supportthe power receiver 105 during the standby phase 515, 517. The powerlevel may be a power level that should be provided continuously or mayfor example be a power level to be provided in a discontinuous mode. Forexample, the power level may be an average power level (and possibly aminimum average power level), which may e.g. be defined by a given dutycycle for a power signal with a given power level and/or as a givenpower level to be applied with a given duty cycle. The standby powersignal requirement may thus provide an indication of the specific powerthat should be provided by the power transmitter 101 when in the standbyphase 515, 517. However, at the same time it can be ensured that thepower consumption of the power transmitter 101 during the standby phase515, 517 can be reduced to the minimum that is required for supportingthe reduced functionality of the power receiver 105.

In many embodiments, the power transmitter 101 may be arranged toprovide a continuous power signal with a reduced power level during thestandby phase 515, 517. The power receiver 105 may (pre)determine howmuch power is consumed when operating in a standby mode where only areduced functionality is powered/active. This power requirement may thenbe communicated to the power transmitter 101 which accordingly proceedsto apply a continuous power signal during the standby phase therebyallowing the power receiver 105 to support the reduced functionalityfrom the power signal while remaining in the standby phase.

Thus, in such an example, the power receiver 105 is continuously poweredwhile in the standby phase with a power signal having reduced power.This allows the power receiver 105 to be kept ready for activationand/or ready to activate the power transmitter 101. For example, acomputational device with no internal power may be placed on a powertransmitter 101 and switched into a standby mode of operation. In thestandby mode of operation the functionality of the computational devicemay be limited to extracting power from the power signal and monitoringfor a user input. This reduced functionality requires very little powerto be provided, and therefore the computational device can prior toentering the standby phase request that a power signal is provided thatis just sufficient to support this reduced functionality and low powerconsumption. Therefore, only very little power is drawn by the powertransmitter 101. When a user provides a user input to wake-up thecomputational device (to transition the computational device from thestandby phase to the operational phase), the computational device maye.g. transmit a wake-up message to the power transmitter 101. Inresponse to receiving the wake-up message, the power transmitter 101exits the standby phase and e.g. moves to the ping phase. The powertransmitter 101 and the power receiver 105/computational device thenproceeds to perform the normal process to enter into the power transferphase in which the power transmitter 101 provides a power signalsufficient to power the normal operation and full functionality of thepower transmitter 101.

Thus, the reduced functionality operated by the power receiver 105during the standby phase may specifically include functionality that caninitialize a wake-up of the power receiver 105. The wake-upfunctionality may initialize the process that allows the power receiver105 to exit the standby phase/standby mode of operation and enter anormal operational phase/mode.

Alternatively or additionally, the reduced functionality operated by thepower receiver 105 during the standby phase 515, 517 may includefunctionality that can initialize a power transfer for the system. Thewake-up functionality may initialize a process that allows the powerreceiver 105 and power transmitter 101 to exit the standby phase 515,517 to enter the power transfer phase 511, 513.

The wake-up functionality may specifically be arranged to wake up/bootup the power receiver 105 and/or to initialize the power transferoperation. Accordingly, the standby power signal requirement for thepower signal during a standby phase may request a power signal thatguarantees a minimal power level for the power receiver allowing atleast its most essential boot-up process to be operated.

In some embodiments, the reduced functionality may include functionalityfor maintaining an energy storage requirement for the power receiverduring the standby phase. The power receiver 105 may contain an energystore, such as a battery or a capacitor holding a charge (which e.g. maybe used to power functionality of the power receiver 105). If no poweris provided to such an energy store, the stored energy will gradually bereduced due to the power consumption of any remaining functionalitypowered by the energy store during the standby phase, or e.g. due tospurious current draws (leakage currents). In the described systems,such energy loss may be compensated during the standby phase by use ofthe power signal provided by the power transmitter 101 in this phase.Thus, the standby power signal requirement may indicate a requirement ofthe power signal which will allow the power receiver 105 to extractpower that can be stored in the energy store. Specifically, tricklecharging may be supported.

The power level requirement may be a predetermined value applied by thepower receiver 105. E.g. the power receiver 105 may be designed totrickle charge its battery during the standby phase with a chargecurrent of, say, 1 mA. In this case, the standby power signalrequirement is set to indicate that a power signal should be providedduring the standby phase from which the power receiver 105 cancontinuously extract a charge current of 1 mA (at the appropriate chargevoltage). In other embodiments, the power receiver 105 may apply morecomplex algorithms to determine a suitable power signal requirement. Forexample, the specific battery status may be determined, and the desiredcharge current may be calculated. The corresponding requirements for thepower signal may then be determined and the standby power signalrequirement set accordingly. The power receiver may indeed in manyembodiments determine the standby power signal requirement in responseto a charge or energy stored status for an energy store powering thepower receiver during standby.

In contrast to the power transfer phase 511, 513, the standby phase 515,517 will typically not include any power control loop. In the powertransfer phase of systems such as Qi, the power receiver 105 transmitspower control errors during the power transfer phase 511, 513. Thesepower control error messages are used to increase or decrease the powerlevel of the power signal as requested by the power receiver 105.However, in the standby phase 515, 517, the functionality, complexityand accordingly power consumption may advantageously be minimized, andthis may include the standby phase 515, 517 not including any powercontrol loop. Thus, the parameters and characteristics of the powersignal may be kept constant during the standby operation.

In the previous examples, a continuous power signal was provided e.g. toallow trickle-charging of a battery thereby allowing the battery to befully charged hours or even days after the charge was completed.Additionally or alternatively, the approach could be used to enable apower receiver without any form of energy storage to remain alert foruser interactions.

In a continuous power standby mode, the power transmitter 101 can keepits operation point constant while providing the standby power to thepower receiver 105. The power receiver 105 does not need to communicateany messages to the power transmitter 101 during standby.

The power transmitter 101 may leave the standby phase 515 when it isinterrupted by an event, e.g. when an active wake-up message is receivedfrom the power receiver 105. Alternatively, the triggering event couldbe a time-out indicating that the ping phase 503 should be entered.Thus, in some embodiments, the system may at regular intervals leave thepowered standby phase 515, 517 to initiate a ping to detect if the powerreceiver 105 requires a power transfer phase to be initialized.

In some embodiments, the power signal may not be provided continuouslybut may be provided intermittently. In some embodiments, a discontinuousprovision of the power signal is used during the standby phase 515, 517,e.g. by providing a power signal in repeating time intervals. In someembodiments, the standby power signal requirement may indicate arequired duty cycle, or equivalently, when the power provision timeintervals are constant, the time interval between the time intervals.Such a discontinuous operation may be more practical and easier toimplement in some embodiments. It may potentially also result in reducedpower consumption.

In a discontinuous standby mode, the power transmitter may provide thepower signal in pulses at equidistant time intervals. The power receivercan communicate the required pulse width, duty cycle and/or time betweenintervals in the standby power signal requirement.

As an example, the Qi standard version 1.0 or version 1.1 may bemodified to enable a power receiver to configure the pulse width as wellas time interval of such a discontinuous power signal of the powertransmitter. The extension can be implemented with a new packet that thepower receiver can communicate during the configuration phase. The powertransmitter may then apply these values when it enters the standbyphase.

The following message may for example be transmitted from the powerreceiver 105 to the power transmitter 101:

b₇ b₆ b₅ b₄ b₃ b₂ b₁ b₀ B₀ Time interval B₁ Pulse width

Time Interval: This field contains an unsigned integer value of the timebetween the start of two succeeding standby power pulses. The leastsignificant bit represents a value of 10 ms. The maximum interval timeis approximately 2.5 seconds.

Pulse Width: This field contains an unsigned integer value of theduration of a standby power pulse. The least significant bit representsa value of 2 ms. The maximum pulse duration is approximately 0.5seconds.

In the previous examples, the power receiver 105 is arranged to extractpower from the power signal during the standby phase. However, althoughthis may be advantageous in many embodiments it is not essential in allembodiments. For example, if an intermittent provision of a power signalduring the standby phase is used in order to allow the power receiver105 to indicate that it desires a power transfer using load modulation,the power receiver 105 may not extract any energy from the power signalbut merely use it to enable communication. In some embodiments, thepower transmitter 101 may provide a signal which is both used forcommunicating a message by load modulation and for powering.

Thus, in some embodiments, the power receiver 105 may be arranged tocommunicate messages to the power transmitter 101 during the standbyphase 515, 517 by load modulating the power signal. This approach mayfor example allow the power receiver 105 to transmit a wake-up messageto the power transmitter 101. Thus, the power signal may be used by thepower receiver 105 to indicate that the standby phase 515, 517 should beterminated and that a power transfer process should be initiated. As thepower signal during the standby phase 515, 517 is controlled by thepower receiver 105, this allows the power receiver 105 to control thepower transmitter 101 to transmit the optimal signal for the specificpower receiver 105.

For example, if an intermittent power signal is provided, the powerreceiver 105 may control the time interval between the intervals inwhich a power signal is provided, and thus it may control the maximumtime between possibilities for transmitting a wake up message by loadmodulation. For a power receiver 105 that requires a very fast poweringup from standby, a power signal is provided with a short time betweenpower signal intervals, whereas for a power receiver 105 that does notrequire fast powering up from standby, a power signal is provided with apotentially much longer time between power signal intervals. Thus, theoperation can be optimized for the individual power receiver 105 andapplication.

In scenarios where an intermittent signal is used to allow messages fromthe power receiver 105 to be provided to the power transmitter 101 byload modulation, each of the power-on intervals may be considered tocorrespond to a ping (similarly to the Qi standard). Thus, the powertransmitter 101 may provide a signal which pings the power receiver 105to see if this wants to exit the standby phase 515, 517. If a wake-upmessage is received in response to the ping (i.e. the power signal beingon in a time interval), the power transmitter 101 may exit the standbyphase 515, 517 to initialize a power transfer. The wake-up message mayfor example be the same message as applied in the conventional pingphase of a Qi system, i.e. the system may follow the protocol andspecifications of the ping phase.

Such a wake-up message may specifically be used to indicate that thepower receiver 105 wants to initiate a charging operation for aninternal energy store. For example, the power receiver 105 maycontinuously monitor the energy storage level of an internal energystore (e.g. the charge of an internal capacitor or battery). If thislevel falls below a given threshold, it is desirable to recharge thebattery. Therefore, initially when the level is above the threshold, thepower receiver 105 responds to the ping provided during the standbyphase 515, 517 with a message that indicates that no power transfer isnecessary. However, if the level falls below the threshold, it proceedsto respond with a message that indicates that a power transfer isrequired. In response, the system initiates a direct or indirecttransition into the power transfer phase 511, 513. The power receiver105 then proceeds to charge the energy store using the power from thepower signal during the power transfer phase 511, 513. When the chargingis complete, the power receiver 105 transmits a message indicating thatno further power transfer is required and that the system should enterthe standby phase 515, 517.

In such an example, the power transmitter 101 provides a ping to thepower receiver 105 which is exploited to recharge the energy storage ofthe power receiver to above a desired level. The ping interval periodcan by the power receiver 105 be set sufficiently short to allow thepower receiver 105 to wake up the power transmitter 101 before the powerstorage of the power receiver 105 is drained too much.

More generally, in response to a ping from the power transmitter 101,the power receiver 105 can indicate if it needs power or not. In case itdoes not need power, it can communicate an end-power packet.

The interval time from the end of one ping to the beginning of the nextcan be controlled by the power receiver 105. Specifically, the powerreceiver 105 can transmit a standby power signal requirement indicatingthe required maximum interval that the power transmitter 101 can applybetween two consecutive pings.

As a specific example of a system that has a high degree ofcompatibility with the Qi system, the power receiver 105 may respond toan initial ping of the ping phase 503, 505 by communication of thenecessary packets as required by the Qi v1.0 standard in order to enterthe identification and configuration phase 507, 509. In this phase, thepower receiver 105 can communicate a configuration packet which includesa standby power signal requirement that indicates whether the powerreceiver 105 requires a minimum ping interval or not during standbyphase.

The power receiver 105 can continue according to the Qi-standard untilit desires to end the power transfer. The end-power-packet from thepower receiver 105 may then indicate whether the power transmitter 101should enter a standby phase 515 with some power signal provision, orwhether it should enter the selection phase 501 where no power signal isprovided.

After entering the standby phase 515, the power transmitter 101 willgenerate a ping with the required time interval. For each ping, thepower receiver 105 can decide whether to respond with a messageterminating the power transfer initialization, in which case the powertransmitter 101 will remain in the standby phase and it will not proceedto the configuration or power phases. In some embodiments, the messageterminating the power transfer initialization may also indicate e.g. anew minimum ping interval time, how the power transmitter shall wake-upfrom the standby mode, etc.

The power receiver 105 may also decide that a power transfer isrequired, in which case it responds to the ping, and the power transferinitialization proceeds.

In some embodiments, the power receiver 105 may not extract any powerfrom the ping signal but only use this as a means for load modulation.However, in some embodiments, the ping signal may be sufficiently strongto allow the power receiver 105 to extract power from the signal. Inthis case, the power receiver 105 may thus not only use the ping signalas a means of communication but also to provide power e.g. to re-chargethe energy store. This may in many scenarios provide increasedflexibility, e.g. by allowing small power provision to be achieved inthe standby phase, together with the option of a very fast, yet passive(load modulation based) initialization of a full power transferoperation.

In another embodiment the power receiver does not provide a wake-upmessage to the power transmitter at all during the standby phase.Instead it requires the power transmitter to power-up from standby phasewithin a period of time. After the system enters the standby phase, thepower transmitter will power up by entering the (normal) ping phaseproviding a power signal at the moment or just before the period ofstandby time exceeds. Thus, the ping phase is executed as part of thestandby phase. This allows the power receiver to recharge its energystore using the normal power signal from the power transmitter. When thecharge is sufficient, the power receiver may indicate to re-enter thestandby phase. In such embodiment, the power transmitter does not haveto provide any power signal during the standby phase except for when theping phase is executed as part of the standby phase. The effectiveresult is equivalent to the situation where the power transmitterprovides an intermitting ping signal during the standby phase,especially if the period of standby time equals to the time intervalbetween the intermitting pings.

The approach may for example be implemented by an extension of the Qistandard v1.0 or 1.1 allowing a power receiver to configure the pingtime interval of the power transmitter in the standby phase. Theextension can be implemented with a new packet that the power receivercommunicates during the configuration phase.

An example of a format of such a message is the following:

b₇ b₆ b₅ b₄ b₃ b₂ b₁ b₀ B₀ Ping Interval Time B₁

Ping Interval Time—the unsigned integer contained in this fieldindicates the interval time between the end of the end power packet andthe start of a new ping. The value is expressed in seconds. In case thepower transmitter removes the power signal by any other means than theend power packet, this field indicates the time between removing thepower signal end the start of a new digital ping. The default value is60 seconds. This value will be used in case the power receiver does notcommunicate this message to the power transmitter.

It will be appreciated that the system may typically enter the standbyphase 515, 517 from the power transfer phase 511, 513. However, in somescenarios, the system may enter the standby phase 515, 517 directly fromthe configuration phase 507, 509 or the ping phase 503, 505 if the powerreceiver 105 e.g. generates and transmits a message indicating that itis not necessary to perform a power transfer. For example, if theprotocol requires or allows the standby power signal requirement to becommunicated as part of a configuration phase message, the powerreceiver 105 may respond to a ping by initiating a power transferprocess via the configuration phase 507, 509. A new standby power signalrequirement may be provided during the configuration phase 507, 509after which the power receiver 105 may send a message indicating thatthe system should return to the standby phase 515, 517 directly withoutproceeding to the power transfer phase 511, 513. This may provide anefficient way of reconfiguring operation in the standby phase 515, 517in many embodiments.

In many embodiments, the system may be arranged to enter the standbyphase 515, 517 from the power transfer phase 511, 513. Specifically, thepower receiver 105 may transmit an end of power transfer phase message(specifically an end of power message (when it no longer requires thepower provision of the power transfer phase 515, 517. In response toreceiving such a message, the power transmitter 101 may enter thestandby phase 515 and start to provide a power signal as defined by apreviously receiver standby power signal requirement (e.g. received aspart of the configuration phase 507, 509). In some embodiments, the endof power transfer phase message may indicate whether the system shouldenter the standby phase 515, 517 or whether it should enter anotherphase (specifically the selection phase 501 where no power signal isprovided).

Specifically, for an enhanced Qi system, the power receiver mayterminate the power transfer phase by transmitting an End Power TransferPacket with the following format:

b₇ b₆ b₅ b₄ b₃ b₂ b₁ b₀ B₀ End Power Transfer Code

End Power Transfer Code: This field identifies the reason for the EndPower Transfer request, as listed in Table 0-2 of the Qi Specificationversion 1.0 and 1.1. The power receiver will typically not transmit EndPower Transfer Packets that contain any of the values that Table 0-2lists as reserved.

However, in the enhanced Qi system, the End Power Transfer Code fieldhas been updated such that it can indicate that the reason forterminating the power transfer phase is that the system should enter thestandby phase.

The End Power Transfer Codes may specifically be:

Reason Value Unknown 0x00 Charge Complete 0x01 Internal Fault 0x02 OverTemperature 0x03 Over Voltage 0x04 Over Current 0x05 Battery Failure0x06 Reconfigure 0x07 No Response 0x08 Standby 0x09 Reserved 0x0A . . .0xFF

The power receiver may use the codes in the following way

-   -   0x00 as specified in Qi version 1.0.    -   0x01 as specified in Qi version 1.0.    -   0x02 as specified in Qi version 1.0.    -   0x03 as specified in Qi version 1.0.    -   0x04 as specified in Qi version 1.0.    -   0x05 as specified in Qi version 1.0.    -   0x06 as specified in Qi version 1.0.    -   0x07 as specified in Qi version 1.0.    -   0x08 as specified in Qi version 1.0.    -   0x09 The Receiver uses this value to indicate that the power        transmitter 101 should enter the standby phase.

In some embodiments, the requirement message may be communicated as partof the power transfer phase 511, 513. For example, it may becommunicated as part of the end of power transfer phase message.

Indeed, in some embodiments the transmission of the end of powertransfer phase message may in itself provide the standby power signalrequirement. For example, in some embodiments, the power receiver 105may at the end of the power transfer phase 511, 513, and in preparationto the standby phase 515, 517, the power receiver 105 may transmitcontrol messages that set the power level of the power signal to adesired level for the power signal during the standby phase 515, 517.Specifically, the power receiver 105 may first switch out the load whileremaining in the power transfer phase 511, 513. It may then proceed totransmit a series of power control error messages that result in thepower level of the power signal being reduced to a desired level for thestandby phase 515, 517. When this level is reached, the power receiver105 transmits the end of power transfer phase message which results inthe power transmitter 101 entering the standby phase 515, 517. The powertransmitter 101 then proceeds to maintain the power signal at thisvalue. Thus, the end of power transfer phase message provides anindication that the current power level of the power signal should bemaintained in the standby phase 515, 517. The power transmitter 101 thenproceeds to maintain this level constant without any power control loop.

In many embodiments, the power receiver 105 may transmit the requirementas part of the configuration phase 507, 509 prior to the power transferphase 511, 513. The configuration phase 507, 509 may in some embodimentsonly be performed prior to the power transfer phase 511, 513 for someinstances of the power transfer phase being initialized (such asspecifically the first time the power receiver 105 proceeds to the powertransfer phase 511, 513 from the standby phase or the ping phase).

The requirement message may thus be provided significantly before thestandby phase 515, 517 is entered and may be part of the generalconfiguration of the operation of the power transfer system. Therequirement may specifically be part of a negotiation subphase of theconfiguration phase 507, 509.

Providing the requirement message as part of the configuration phase507, 509 may allow facilitated operation in many embodiments, and mayoften reduce the modifications required to existing systems andstandards to support the introduction of a standby phase as described.

Furthermore, the system may be arranged to configure several otheraspects of the operation of the system in connection with the standbyphase 515, 517 (typically but not necessarily as part of theconfiguration phase 507, 509 (and specifically the negotiationsubphase).

For example, the power receiver 105 may configure the power transmitter101 to perform an activity to be performed by the power transmitter whenexiting the standby phase 515, 517.

Specifically, if the power transmitter 101 receives an active or passivewake up message, it will exit the standby phase 515, 517.

In many embodiments, the system may exit the standby phase 51, 517 toenter the ping phase 503, 505. The system may then proceed to use thesame approach for setting up a power transfer as when the system entersthe ping phase 503, 505 from the selection phase 501. Such an approachmay allow the same approach to be followed, and may provide improvedbackwards compatibility, robustness, facilitated implementation and/orreduced complexity.

In other embodiments, the process causing the system to exit the standbyphase 515, 517 may correspond to the process performed in the ping phase503, 505. For example, when pings are used in the standby phase 515,517, these may correspond to those used in the ping phase 503, 505, andthe same protocols etc. may be used. Therefore, there is no need torepeat the process by entering the ping phase 503, 505, and in someembodiments the system therefore enters the configuration phase 507, 509directly from the standby phase 515, 517.

In some embodiments, the operation may further skip the configurationphase 507, 509. Thus, in some embodiments, the power transmitter 101 andpower receiver 105 may directly enter the power transfer phase 511, 513when exiting the standby phase 515, 517. Such an approach may allow amuch faster and more efficient initialization of a power transfer phase511, 513. This may be particularly suitable for scenarios whereinrelatively short but frequent power transfer phase operations are used(e.g. to maintain charge in a capacitor). However, a downside is thatthe power transfer is not (re)configured for the individual powertransfer phase execution. Typically, the power transmitter 101 willproceed to apply the parameters from the termination of the previouspower transfer phase 511, 513. As another example, the power transferphase 511, 513 may be initiated with nominal parameter values.

The different approaches may have different advantages anddisadvantages.

In some embodiments, the power receiver 105 may control how the powertransmitter 101 should exit the standby phase, and specifically whetherthe configuration phase should be skipped.

This may specifically be configured during the configuration phase 507,509. The configuration phase 507, 509 may for example also be used todefine whether continuous or discontinuous operation should be used,whether active or passive wake-up messages are used etc.

It will be appreciated that the same message may be used to provide suchconfiguration data and to provide the standby power signal requirement.

Specifically, the power receiver 105 may during the configuration phasecommunicate configuration information in order to instruct the powertransmitter

-   -   at which event the power transmitter 101 has to wake-up,        specifically if wake up is provide as an active wake-up signal        or as a passive wake up signal;    -   whether the power transmitter 101 has to provide a standby power        signal during the standby phase 515,        -   and whether this standby power signal has to be continuous            or discontinuous;        -   and if discontinuous what the timing requirements are (e.g.            the maximum interval between pings);    -   how the power transmitter has to resume after wake-up,        specifically whether to exit the standby phase to directly enter        the power transfer phase or whether to enter the configuration        phase.

The following describes an exemplary extension of the Qi standard toenable a power receiver to configure the standby mode of a powertransmitter. The extension can be implemented by adding sixconfiguration bits to the existing configuration message defined in theQi specification version 1.0.

b₇ b₆ b₅ b₄ b₃ b₂ b₁ b₀ B₀ Power Class Maximum Power B₁ Reserved B₂ PropReserved Count B₃ WkUp WkUp Ping Stdby Cont R2PT A B B₄ Reserved

Power Class as specified in Qi version 1.0.

Maximum Power as specified in Qi version 1.0

Prop as specified in Qi version 1.0.

WkUpA if this bit is set to ONE, the power transmitter shall wake-upfrom standby on an active wake-up signal provided by the power receiver.

WkUpB if this bit is set to ONE, the power transmitter shall wake-upfrom standby on a passive wake-up signal provided by the power receiver,which could be impedance change/load modulation provided by the powerreceiver.

Ping If this bit is set to ONE, the power transmitter shall start a newping within t_(pinginterval) after receiving (the end of) the end-powerpacket indicating to enter the standby mode, or otherwise after removingthe power signal.

Stdby If this bit is set to ONE, the power transmitter provides astandby power signal to the power receiver after receiving an end-powerpacket indicating to enter the standby mode. If this bit is set to ZERO,the power transmitter does not provide a standby power signal afterreceiving an end power packet, regardless of the content of this packet.

Cont If this bit is set to ONE, the standby power signal shall becontinuous. If this bit is set to ZERO the standby power signal shall bediscontinuous.

R2PT If this bit is set to ONE, the power transmitter returns to thepower transfer mode after the detection of a wake-up signal from thepower receiver. If another event has interrupted the power transmitterbefore, the power transmitter starts with a ping. The power transmitterhas to ensure that the power receiver is still present.

Reserved as specified in Qi version 1.0.

Count as specified in Qi version 1.0.

The previous description has focused on describing the standby phase515, 517 as a completely separate phase of the selection phase 501 andthe ping phase 503, 505. However, it will be appreciated that in someembodiments, the operation in the phases may be very similar and indeedthere may be some overlap between the phases, and that the samefunctionality may be used in more than one of the phases.

For example, the pings provided in the standby phase 515, 517 maycorrespond directly to the pings provided in the ping phase 503, 505,and indeed the standby phase 515, 517 may in some scenarios beconsidered to provide a parallel operation as the ping phase 503, 505but being controlled by the standby power signal requirement from thepower receiver 105.

Indeed, in some embodiments where a discontinuous power signal andpassive load modulation is used, the standby phase 515, 517 can beimplemented by switching the power transmitter 101 between the selectionphase 501 and the ping phase 503, 505 in accordance with the standbypower signal requirement from the power receiver 105.

Specifically, if the selection phase 501 is implemented as onecomputational process and the ping phase 503, 505 is implemented as asecond computational process, the standby phase 515, 517 may beimplemented by the power transmitter 101 executing the firstcomputational process and switching temporarily to the secondcomputational process at intervals given by the timing indicationprovided by the standby power signal requirement.

Thus, in some embodiments, the standby phase may include sub-phases,such as for example other Qi phases. Specifically, the standby phase mayconsist or comprise in the selection phase and the ping phase. In suchembodiments, the first message from the power receiver 105 may provide atiming indication relating to the transitioning between the selectionphase and the ping phase.

For example, the standby phase may consist in the selection phase andthe ping phase. The power transmitter 101 may enter the standby phase byfirst entering the selection phase. It then remains in the selectionphase until it transitions to the ping phase (which is also consideredpart of the standby phase). The timing of this transition may bedetermined by the first message from the receiver which specifically mayindicate a maximum duration for the selection phase before entering theping phase. In the example, the power signal provided in the standbyphase thus corresponds to the power signal when in the ping (sub)phasewith no power signal being provided when in the selection (sub)phase.Thus, in the example, the message from the power receiver 105 indicateshow the power signal in the standby phase (comprising the selectionphase and the ping phase) should be operated by providing timinginformation for transitions from the selection phase to the ping phase.

In the example, a new message is thus introduced which informs the powertransmitter of the maximum allowed interval between ping phases. Thepower transmitter proceeds to operate in the selection phase butswitches to the ping phase as indicated by the message. The powerreceiver 105 may then initiate an exit from the standby phase byproceeding to the configuration or power transfer phase. Alternatively,the system may remain in the standby phase and may accordingly return tothe selection phase. When it has been in this phase for the durationindicated by the message, the power transmitter 101 may again enter theping phase etc.

It will be appreciated that the above description for clarity hasdescribed embodiments of the invention with reference to differentfunctional circuits, units and processors. However, it will be apparentthat any suitable distribution of functionality between differentfunctional circuits, units or processors may be used without detractingfrom the invention. For example, functionality illustrated to beperformed by separate processors or controllers may be performed by thesame processor or controllers. Hence, references to specific functionalunits or circuits are only to be seen as references to suitable meansfor providing the described functionality rather than indicative of astrict logical or physical structure or organization.

The invention can be implemented in any suitable form includinghardware, software, firmware or any combination of these. The inventionmay optionally be implemented at least partly as computer softwarerunning on one or more data processors and/or digital signal processors.The elements and components of an embodiment of the invention may bephysically, functionally and logically implemented in any suitable way.Indeed the functionality may be implemented in a single unit, in aplurality of units or as part of other functional units. As such, theinvention may be implemented in a single unit or may be physically andfunctionally distributed between different units, circuits andprocessors.

Although the present invention has been described in connection withsome embodiments, it is not intended to be limited to the specific formset forth herein. Rather, the scope of the present invention is limitedonly by the accompanying claims. Additionally, although a feature mayappear to be described in connection with particular embodiments, oneskilled in the art would recognize that various features of thedescribed embodiments may be combined in accordance with the invention.In the claims, the term comprising does not exclude the presence ofother elements or steps.

Furthermore, although individually listed, a plurality of means,elements, circuits or method steps may be implemented by e.g. a singlecircuit, unit or processor. Additionally, although individual featuresmay be included in different claims, these may possibly beadvantageously combined, and the inclusion in different claims does notimply that a combination of features is not feasible and/oradvantageous. Also the inclusion of a feature in one category of claimsdoes not imply a limitation to this category but rather indicates thatthe feature is equally applicable to other claim categories asappropriate. Furthermore, the order of features in the claims do notimply any specific order in which the features must be worked and inparticular the order of individual steps in a method claim does notimply that the steps must be performed in this order. Rather, the stepsmay be performed in any suitable order. In addition, singular referencesdo not exclude a plurality. Thus references to “a”, “an”, “first”,“second” etc. do not preclude a plurality. Reference signs in the claimsare provided merely as a clarifying example shall not be construed aslimiting the scope of the claims in any way.

The invention claimed is:
 1. A method of operating an inductive powertransfer system, the method comprising: generating, by a powertransmitter, a wireless signal for a power receiver when in a powertransfer phase; transmitting, by the power receiver, a first message tothe power transmitter, the first message comprising a standby signalrequirement for the wireless signal during a standby phase; receiving,by the power transmitter, the first message; and providing, by the powertransmitter, the wireless signal in accordance with the standby signalrequirement during the standby phase, wherein the power receiverdetermines an energy storage level for the power receiver and transmitsa second message to the power transmitter during the standby phase ifthe energy storage level is below a threshold, and wherein the powerreceiver and the power transmitter initiate a power transfer operationif the second message is transmitted.
 2. A method of operating aninductive power transfer system, the method comprising: generating, by apower transmitter, a wireless signal for a power receiver when in apower transfer phase; transmitting, by the power receiver, a firstmessage to the power transmitter, the first message comprising a standbysignal requirement for the wireless signal during a standby phase;receiving, by the power transmitter, the first message; and providing,by the power transmitter, the wireless signal in accordance with thestandby signal requirement during the standby phase, wherein the powerreceiver sets a power level for the wireless signal by transmittingpower control error messages at the end of the power transfer phase, andthe standby signal requirement is indicative of a requirement tomaintain the power level during the standby phase.
 3. An inductive powertransfer system comprising a power transmitter and a power receiver, theinductive power transfer system being arranged to transfer power fromthe power transmitter to the power receiver via a wireless signal andsupporting communication from the power receiver to the powertransmitter based on load modulation of the wireless signal, wherein thepower receiver comprises a transmitter for transmitting a first messageto the power transmitter, the first message comprising a standby signalrequirement for the wireless signal during a standby phase; and thepower transmitter comprises: a power unit for generating the wirelesssignal to provide power transfer to the power receiver when in a powertransfer phase: a receiver for receiving the first message; and astandby unit for providing the wireless signal in accordance with thestandby signal requirement during the standby phase.
 4. A powertransmitter for an inductive power transfer system comprising the powertransmitter and a power receiver, the inductive power transfer systemsupporting communication from the power receiver to the powertransmitter based on load modulation of a wireless signal, the powertransmitter comprising: a generator for generating the wireless signalfor the power receiver when in a power transfer phase; a receiver forreceiving a first message comprising a standby signal requirement forthe wireless signal during a standby phase; and a standby unit forproviding the wireless signal in accordance with the standby signalrequirement during the standby phase.